1. Field of the Invention
This invention relates generally to apparatus and methods for enabling a blind person to determine the status of a plurality of telephone lines from the illumination condition of signal lamps respectively associated therewith.
2. Description of the Prior Art
Conventional, multi-line business telephone instruments have a plurality of line selector push-buttons, each push-button having a lamp associated therewith for visually indicating the status of its particular line. These lamps typically indicate four line status conditions, i.e., "ON" with the particular lamp having a steady state illumination indicating that the respective line is in use; "OFF" with the particular lamp off indicating that the respective line is not in use; "RINGING" with the particular lamp flashing at a one per second repetition rate indicating that the respective line is ringing, and; "HOLD" with the particular lamp flashing at a two per second repetition rate indicating that the respective line has been placed in the "HOLD" status; manifestly, a blind person in attempting to determine a particular line having an incoming call, or in attempting to locate a vacant line, may interrupt a conversation on another particular line or disconnect a line which is in the "HOLD" status.
U.S. Patent Application Ser. No. 657,719, filed Feb. 13, 1976, now U.S. Pat. No. 4,028,502, by the present applicants, and assigned to the assignee of the present application, discloses vibratory push-button apparatus for providing auditory and tactile recognition of an indicator lamp associated with a line selector push-button of a multi-line telephone instrument. While the apparatus of the aforesaid application is satisfactory for some purposes, it has been found to have several deficiencies including an inconveniently long period of time required to identify active lines when several push-buttons are vibrating simultaneously, sensitivity to ambient light, and the non-harmonious character of the push-button vibration.
It is accordingly desirable to provide an apparatus and method for monitoring the illumination condition of the indicator lamps of a multi-line telephone instrument which provides an acoustic output which is uniquely different for each line. More particularly, it is desirable to provide such a system in which the "HOLD" and "RING" status of each line is differentiated by a tone having a tone duration uniquely different for each line, the "HOLD" status of a particular line being indicated by a pulsating modulation superimposed on the basic tone, the "ON" status of the several lines being determined by a user-controlled interrogation function. Finally, it is desirable that such an apparatus and method require no electrical connection and minimal mechanical attachment to the telephone instrument.